Such measurements, e.g., the "Drager DLE Method," are currently carried out by allowing a carrier gas, e.g., air, to flow through a sample of the liquid containing the gas to be measured in a wash bottle, so that the carrier gas takes up the gaseous substance to be measured, especially a volatile harmful substance. The carrier gas may be passed first through a prefilter, especially an activated carbon tube, for precleaning, and it is then pumped by means of a pump to the gas-measuring apparatus, and the wash bottle with the liquid sample, through which the pure carrier flows, is arranged between the prefilter and the gas-measuring apparatus. The immersion tube of the wash bottle is provided with a frit in order to achieve a fine distribution of the gas in the liquid and consequently the highest possible degree of saturation of the carrier gas. The saturation of the carrier gas with the gas to be determined depends on various parameters, especially the size of the gas bubbles, the temperature, and the residence time in the liquid. Special devices, individual calibration, and correction at the time of the evaluation of the measurement results are necessary as a result. A more detailed description of this can be found in the Drager inhouse publication Analytik von Schadstoffen in flussigen Proben Analysis of Harmful Substances in Liquid Samples!. The determination of the gas concentration proper is carried out in a gas-measuring apparatus, especially one comprising a visually or optoelectronically scanned test tube with a color reaction zone providing a substance-specific and concentration-dependent display, wherein the length of the change in color indicated is usually an indicator of the concentration of the gas to be detected.